Low Non-Linear Loss Silicon Waveguides with Sweep-Out Diodes

ABSTRACT

An optical waveguide includes a core region extending substantially along a lengthwise centerline of the optical waveguide, a first cladding region formed along a first side of the core region, and a second cladding region formed along a second side of the core region. The optical waveguide includes a first diode segment and a second diode segment that each include respective portions of the core region, the first cladding region, and the second cladding region. The second diode segment is contiguous with the first diode segment. The first diode segment forms a first diode across the optical waveguide such that a first intrinsic electric field extends across the first diode segment in a first direction, and the second diode segment forms a second diode across the optical waveguide such that a second intrinsic electric field extends across the second diode segment in a second direction opposite the first direction.

CLAIM OF PRIORITY

This application is a continuation application under 35 U.S.C. 120 ofprior U.S. Non-Provisional patent application Ser. No. 17/696,823, filedon Mar. 16, 2022, issued as U.S. Pat. No. 11,733,554, on Aug. 22, 2023,which claims priority under 35 U.S.C. 119 to U.S. Provisional PatentApplication No. 63/161,994, filed on Mar. 17, 2021. The disclosure ofeach above-identified patent application is incorporated herein byreference in its entirety for all purposes.

BACKGROUND 1. Field of the Invention

The disclosed embodiments relate to optical data communication.

2. Description of the Related Art

Optical data communication systems operate by modulating laser light toencode digital data patterns. The modulated laser light is transmittedthrough an optical data network from a sending node to a receiving node.The modulated laser light having arrived at the receiving node isde-modulated to obtain the original digital data patterns. Therefore,implementation and operation of optical data communication systems isdependent upon having reliable and efficient devices for conveyingoptical signals, modulating optical signals, and receiving opticalsignals. It is within this context that the disclosed embodiments arise.

SUMMARY

In an example embodiment, an optical waveguide is disclosed. The opticalwaveguide includes a core region extending substantially along alengthwise centerline of the optical waveguide that corresponds to alight propagation direction through the optical waveguide. The opticalwaveguide also includes a first cladding region formed along a firstside of the core region. The optical waveguide also includes a secondcladding region formed along a second side of the core region. Theoptical waveguide includes a first diode segment and a second diodesegment that each include respective portions of the core region, thefirst cladding region, and the second cladding region. The second diodesegment is contiguous with the first diode segment. The first diodesegment is configured to form a first diode across the opticalwaveguide, such that a first intrinsic electric field extends across thefirst diode segment in a first direction substantially perpendicular tothe lengthwise centerline of the optical waveguide. The second diodesegment is configured to form a second diode across the opticalwaveguide, such that a second intrinsic electric field extends acrossthe second diode segment in a second direction opposite the firstdirection. A first electrical conductor is disposed to electricallyconnect the first diode segment and the second diode segment at alocation on the first side of the core region. A second electricalconductor is disposed to electrically connect the first diode segmentand the second diode segment at a location on the second side of thecore region.

In an example embodiment, an optical waveguide is disclosed. The opticalwaveguide includes a core region that extends substantially along alengthwise centerline of the optical waveguide that corresponds to alight propagation direction through the optical waveguide. The opticalwaveguide also includes a first cladding region formed along a firstside of the core region. The optical waveguide also includes a secondcladding region formed along a second side of the core region. Theoptical waveguide includes an N-doped region, a P-doped region, and anintrinsic region located between the N-doped region and the P-dopedregion. The N-doped region includes a first lengthwise section formedwithin the first cladding region, a second lengthwise section formedwithin the second cladding region, and a crosswise section formed toextend between the first lengthwise section and the second lengthwisesection of the N-doped region. The P-doped region includes a firstlengthwise section formed within the second cladding region, a secondlengthwise section formed within the first cladding region, and acrosswise section formed to extend between the first lengthwise sectionand the second lengthwise section of the P-doped region. A firstelectrical conductor is disposed to electrically connect the firstlengthwise section of the N-doped region and the second lengthwisesection of the P-doped region at a location above the first claddingregion. A second electrical conductor is disposed to electricallyconnect the first lengthwise section of the P-doped region and thesecond lengthwise section of the N-doped region at a location above thesecond cladding region. The first lengthwise section of the N-dopedregion, the first lengthwise section of the P-doped region, and theintrinsic region collectively form a PIN diode across the opticalwaveguide. The first electrical conductor and the second electricalconductor collectively close an electrical loop between the N-dopedregion and the P-doped region, such that an intrinsic electric fieldextends across the core region from the N-doped region to the P-dopedregion.

In an example embodiment, a method is disclosed for reducing opticalloss within an optical waveguide. The method includes having an opticalwaveguide that includes a core region, a first cladding region, and asecond cladding region. The core region extends substantially along alengthwise centerline of the optical waveguide that corresponds to alight propagation direction through the optical waveguide. The firstcladding region is formed along a first side of the core region. Thesecond cladding region is formed along a second side of the core region.The optical waveguide includes a first diode segment and a second diodesegment that each includes respective portions of the core region, thefirst cladding region, and the second cladding region. The second diodesegment is contiguous with the first diode segment. The first diodesegment is configured to form a first diode across the opticalwaveguide, such that a first intrinsic electric field extends across thefirst diode segment in a first direction substantially perpendicular tothe lengthwise centerline of the optical waveguide. The second diodesegment is configured to form a second diode across the opticalwaveguide, such that a second intrinsic electric field extends acrossthe second diode segment in a second direction opposite the firstdirection. The optical waveguide also includes a first electricalconductor disposed to electrically connect the first diode segment andthe second diode segment at a location on the first side of the coreregion. The optical waveguide also includes a second electricalconductor disposed to electrically connect the first diode segment andthe second diode segment at a location on the second side of the coreregion. The method also includes transmitting light through the coreregion of the optical waveguide, such that some of the light generatesfree-carriers within the core region, where the generated free-carriersare swept out of the core region within the first diode segment of theoptical waveguide by the first intrinsic electric field, and where thegenerated free-carriers are swept out of the core region within thesecond diode segment of the optical waveguide by the second intrinsicelectric field.

In an example embodiment, a method is disclosed for manufacturing anoptical conveyance device. The method includes forming an opticalwaveguide that includes a core region, a first cladding region, and asecond cladding region. The core region extends substantially along alengthwise centerline of the optical waveguide that corresponds to alight propagation direction through the optical waveguide. The firstcladding region is formed along a first side of the core region. Thesecond cladding region is formed along a second side of the core region.The method also includes forming a first diode within a first diodesegment of the optical waveguide. The first diode segment includes afirst portion of the core region, a first portion of the first claddingregion, and a first portion of the second cladding region. The firstdiode includes an N-doped region formed within the first portion of thefirst cladding region and a P-doped region formed within the firstportion of the second cladding region, such that a first intrinsicelectric field extends through the first portion of the core region in afirst direction substantially perpendicular to the lengthwise centerlineof the optical waveguide. The method also includes forming a seconddiode within a second diode segment of the optical waveguide. The seconddiode segment includes a second portion of the core region, a secondportion of the first cladding region, and a second portion of the secondcladding region. The second diode includes a P-doped region formedwithin the second portion of the first cladding region and an N-dopedregion formed within the second portion of the second cladding region,such that a second intrinsic electric field extends through the secondportion of the core region in a second direction opposite of the firstdirection. The method also includes electrically connecting the N-dopedregion of the first diode to the P-doped region of the second diode. Themethod also includes electrically connecting the P-doped region of thefirst diode to the N-doped region of the second diode.

Other aspects and advantages of the disclosed embodiments will becomemore apparent from the following detailed description, taken inconjunction with the accompanying drawings, illustrating by way ofexample the disclosed embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows a top view of an optical waveguide, in accordance withsome embodiments.

FIG. 1B shows a vertical cross-section view through the opticalwaveguide, referenced as View A-A in FIG. 1A, in accordance with someembodiments.

FIG. 2A shows a top view of an optical waveguide, in accordance withsome embodiments.

FIG. 2B shows a vertical cross-section view through the opticalwaveguide, referenced as View A-A in FIG. 2A, in accordance with someembodiments.

FIG. 2C shows a vertical cross-section view through the opticalwaveguide, referenced as View B-B in FIG. 2A, in accordance with someembodiments.

FIG. 2D shows the top view of the optical waveguide of FIG. 2A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region by the diodes of the first diodesegment, the second diode segment, the third diode segment, and thefourth diode segment, in accordance with some embodiments.

FIG. 2E shows a curved portion of the optical waveguide, in accordancewith some embodiments.

FIG. 2F shows a vertical cross-section view through the opticalwaveguide, referenced as View C-C in FIG. 2E, in accordance with someembodiments.

FIG. 2G shows plots of optical angular propagation constant as afunction the radius of curvature of the lengthwise centerline of theoptical waveguide for the primary optical mode within the core regionand the primary optical mode in the second outer cladding region forvarious widths of the second outer cladding region, in accordance withsome embodiments.

FIG. 3 shows simulation results of free-carrier build-up in the coreregion at different optical powers for various embodiments of theoptical waveguide of FIGS. 2A-2F in which the width of the intrinsicregions is modified, in accordance with some embodiments.

FIG. 4A shows a top view of an optical waveguide, in accordance withsome embodiments.

FIG. 4B shows a vertical cross-section view through the opticalwaveguide, referenced as View A-A in FIG. 4A, in accordance with someembodiments.

FIG. 4C shows a vertical cross-section view through the opticalwaveguide, referenced as View B-B in FIG. 4A, in accordance with someembodiments.

FIG. 4D shows the top view of the optical waveguide of FIG. 4A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region by the diodes of the first diodesegment, the second diode segment, the third diode segment, and thefourth diode segment, in accordance with some embodiments.

FIG. 5A shows a top view of an optical waveguide, in accordance withsome embodiments.

FIG. 5B shows a vertical cross-section view through the opticalwaveguide, referenced as View A-A in FIG. 5A, in accordance with someembodiments.

FIG. 5C shows a vertical cross-section view through the opticalwaveguide, referenced as View B-B in FIG. 5A, in accordance with someembodiments.

FIG. 5D shows a vertical cross-section view through the opticalwaveguide, referenced as View C-C in FIG. 5A, in accordance with someembodiments.

FIG. 5E shows a vertical cross-section view through the opticalwaveguide, referenced as View D-D in FIG. 5A, in accordance with someembodiments.

FIG. 5F shows a vertical cross-section view through the opticalwaveguide, referenced as View E-E in FIG. 5A, in accordance with someembodiments.

FIG. 5G shows the top view of the optical waveguide of FIG. 5A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region by the diode segment, in accordancewith some embodiments.

FIG. 6 shows a flowchart of a method for reducing optical loss within anoptical waveguide, in accordance with some embodiments.

FIG. 7 shows a flowchart of a method for manufacturing an opticalconveyance device, in accordance with some embodiments.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide an understanding of the disclosed embodiments. It willbe apparent, however, to one skilled in the art that the disclosedembodiments may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the disclosedembodiments.

Since the bandgap energy of silicon is larger than that of photons attelecom frequencies, optical (light) absorption losses of siliconoptical waveguides are typically negligible. However, the energy of twophotons does exceed the bandgap energy of silicon and can cause what isknown as two-photon absorption (TPA) in silicon optical waveguides. Thelikelihood of two photons being absorbed in a silicon optical waveguideincreases quadratically with the intensity of light propagating thoughthe silicon optical waveguide. Therefore, TPA in the silicon opticalwaveguide is a second order optical absorption effect and is pronouncedat higher optical power. While TPA introduces an additional optical lossterm, increased free-carrier density generation in the silicon opticalwaveguide can be an even more significant contributor to linear opticalloss in the silicon optical waveguide at higher optical powers. Thefree-carriers (electrons and holes) generated within the silicon opticalwaveguide produce high free-carrier optical absorption losses. Thefree-carrier optical absorption optical loss is linear loss created by asecond-order process and is thus a third-order effect. The opticalabsorption loss in the optical waveguide due to TPA and free-carrieroptical absorption is represented in Equation 1, where I is the lightintensity, z is the light propagation distance along the opticalwaveguide, a′ is the linear optical loss coefficient due tofree-carriers within the optical waveguide, τ is the free-carrierlifetime within the optical waveguide, and β′ is the TPA coefficient.

(I/z)=−a′·τ·β′I ³  Equation 1.

The free-carrier lifetime r within the optical waveguide is a keyparameter, which can be reduced in various ways. For example, in someembodiments, the optical waveguide fabrication is adjusted to increasethe free-carrier recombination rate in silicon and correspondinglyreduce the free-carrier lifetime r within the silicon optical waveguide.In some embodiments, free-carriers are removed from the opticalwaveguide by an electric field. More specifically, an electric field isformed across the optical waveguide, and this electric field pulls thecharged free-carriers (electrons and holes) away from a core region ofthe optical waveguide through which the primary optical mode propagates,so that the charged free-carriers cannot cause optical absorption losswithin the core region. This process is known as carrier sweep out andcan significantly reduce optical losses that scale with free-carrierconcentration, such as the above-mentioned third-order opticalabsorption losses. In some embodiments, diodes operated in reverse biasmode are used to generate the electric field across the opticalwaveguide for carrier sweep out.

FIG. 1A shows a top view of an optical waveguide 100, in accordance withsome embodiments. FIG. 1B shows a vertical cross-section view throughthe optical waveguide 100, referenced as View A-A in FIG. 1A, inaccordance with some embodiments. In some embodiments, the opticalwaveguide 100 is formed of silicon. In some embodiments, the opticalwaveguide 100 is surrounded by one or materials that have a differentoptical index of refraction than that of the material used to form theoptical waveguide 100. For example, in some embodiments, the opticalwaveguide 100 is formed of silicon and is surrounded by silicon dioxide.It should be understood that in various embodiments, the opticalwaveguide 100 formed of silicon can be surrounded by essentially anyoptical cladding material that has an optical index of refractiondifferent than silicon.

The optical waveguide 100 includes a core region 103, a first claddingregion 102, and a second cladding region 104. In some embodiments, thecore region 103, the first cladding region 102, and the second claddingregion 104 are formed as respective parts of a monolithic structure. Thecore region 103 is formed between the first cladding region 102 and thesecond cladding region 104, across a width 101 of the optical waveguide100. The core region 103 extends substantially along a lengthwisecenterline 106 of the optical waveguide 100. The lengthwise centerline106 of the optical waveguide 100 corresponds to a light propagationdirection 149 through the optical waveguide 100. In some embodiments,the first cladding region 102 includes a first inner cladding region 105and a first outer cladding region 109. The first inner cladding region105 extends between the core region 103 and the first outer claddingregion 109. In some embodiments, a thickness 113 of the first outercladding region 109 is greater than a thickness 115 of the first innercladding region 105.

In some embodiments, the second cladding region 104 includes a secondinner cladding region 107 and a second outer cladding region 111. Thesecond inner cladding region 107 extends between the core region 103 andthe second outer cladding region 111. In some embodiments, a thickness117 of the second outer cladding region 111 is greater than a thickness119 of the second inner cladding region 107. In some embodiments, athickness 121 of the core region 103 is greater than the thickness 115of the first inner cladding region 105. Also, in some embodiments, thethickness 121 of the core region 103 is greater than the thickness 119of the second inner cladding region 107. In some embodiments, thethickness 119 of the second inner cladding region 107 is substantiallyequal to the thickness 115 of the first inner cladding region 105. Insome embodiments, the thickness 117 of the second outer cladding region111 is substantially equal to the thickness 113 of the first outercladding region 109. In some embodiments, the optical waveguide 100 isreferred to as a rib waveguide due to the reduced thickness 115 of thefirst inner cladding region 105 and the reduced thickness 119 of thesecond inner cladding region 107.

Light travels through the core region 103 of the optical waveguide 100in the light propagation direction 149. At higher optical power levels,the light traveling through the core region 103 causes TPA, whichgenerates free-carriers (electrons (e) and holes (h)) within the coreregion 103. The free-carriers generated in the core region 103 in turncause free-carrier optical absorption of the light traveling through thecore region 103, which results in high optical loss within the opticalwaveguide 100. Therefore, it is of interest to remove the free-carriersthat are generated by TPA from the core region 103 in order to reducethe free-carrier optical absorption of the light traveling through thecore region 103. Various embodiments are disclosed herein for modifyingthe optical waveguide 100 to create an intrinsic electric field acrossthe core region 103 that serves to pull/sweep out the free-carriers fromwithin the core region 103, so as to reduce the free-carrier opticalabsorption of the light traveling through the core region 103.

FIG. 2A shows a top view of an optical waveguide 200, in accordance withsome embodiments. FIG. 2B shows a vertical cross-section view throughthe optical waveguide 200, referenced as View A-A in FIG. 2A, inaccordance with some embodiments. FIG. 2C shows a vertical cross-sectionview through the optical waveguide 200, referenced as View B-B in FIG.2A, in accordance with some embodiments. The optical waveguide 200 is amodification of the optical waveguide 100. The optical waveguide 200includes the core region 103, the first cladding region 102, and thesecond cladding region 104 as described with regard to FIGS. 1A-1B. Thefirst cladding region 102 is formed along a first side of the coreregion 103. The second cladding region 104 is formed along a second sideof the core region 103. The optical waveguide 200 includes a first diodesegment 241, a second diode segment 242, a third diode segment 243, anda fourth diode segment 244. Each of the first diode segment 241, thesecond diode segment 242, the third diode segment 243, and the fourthdiode segment 244 includes respective portions of the core region 103,the first cladding region 102, and the second cladding region 104. Insome embodiments, the second diode segment 242 is contiguous with boththe first diode segment 241 and the third diode segment 243, and thefourth diode segment 244 is contiguous with the third diode segment 243.It should be understood that for ease of description FIG. 2A depicts aportion of the optical waveguide 200. The pattern of the configurationsof the first diode segment 241, the second diode segment 242, the thirddiode segment 243, and the fourth diode segment 244 continues along thelength of the optical waveguide 200. Therefore, in various embodiments,the optical waveguide 200 includes many more than just the four diodesegments 241, 242, 243, and 244.

The first diode segment 241 is configured to form a first diode acrossthe optical waveguide 200 such that a first intrinsic electric field E1extends across the first diode segment 241 in a first direction 251substantially perpendicular to the lengthwise centerline 106 of theoptical waveguide 200. The second diode segment 242 is configured toform a second diode across the optical waveguide 200 such that a secondintrinsic electric field E2 extends across the second diode segment 242in a second direction 252 opposite the first direction 251. The thirddiode segment 243 is configured to form a third diode across the opticalwaveguide 200 such that a third intrinsic electric field E3 extendsacross the third diode segment 243 in a third direction 253 opposite thesecond direction 252. The fourth diode segment 244 is configured to forma fourth diode across the optical waveguide 200 such that a fourthintrinsic electric field E4 extends across the fourth diode segment 244in a fourth direction 254 opposite the third direction 253.

In some embodiments, a first electrical conductor 229 is disposed toelectrically connect the first diode segment 241 and the second diodesegment 242 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a secondelectrical conductor 231 is disposed to electrically connect the firstdiode segment 241 and the second diode segment 242 at a location overthe second cladding region 104 on the second side of the core region103. In some embodiments, the first electrical conductor 229 is formedas a region of silicide, and the second electrical conductor 231 isformed as another region of silicide. In some embodiments, the firstelectrical conductor 229 is formed as an electrically conductivestructure disposed on both a region of the first diode segment 241 and aregion of the second diode segment 242, and the second electricalconductor 231 is formed as an electrically conductive structure disposedon both a region of the first diode segment 241 and a region of thesecond diode segment 242.

In some embodiments, a third electrical conductor 233 is disposed toelectrically connect the second diode segment 242 and the third diodesegment 243 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a fourthelectrical conductor 235 is disposed to electrically connect the seconddiode segment 242 and the third diode segment 243 at a location over thesecond cladding region 104 on the second side of the core region 103. Insome embodiments, the third electrical conductor 233 is formed as aregion of silicide, and the fourth electrical conductor 235 is formed asanother region of silicide. In some embodiments, the third electricalconductor 233 is formed as an electrically conductive structure disposedon both a region of the second diode segment 242 and a region of thethird diode segment 243, and the fourth electrical conductor 235 isformed as an electrically conductive structure disposed on both a regionof the second diode segment 242 and a region of the third diode segment243.

In some embodiments, a fifth electrical conductor 237 is disposed toelectrically connect the third diode segment 243 and the fourth diodesegment 244 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a sixthelectrical conductor 239 is disposed to electrically connect the thirddiode segment 243 and the fourth diode segment 244 at a location overthe second cladding region 104 on the second side of the core region103. In some embodiments, the fifth electrical conductor 237 is formedas a region of silicide, and the sixth electrical conductor 239 isformed as another region of silicide. In some embodiments, the fifthelectrical conductor 237 is formed as an electrically conductivestructure disposed on both a region of the third diode segment 243 and aregion of the fourth diode segment 244, and the sixth electricalconductor 239 is formed as an electrically conductive structure disposedon both a region of the third diode segment 243 and a region of thefourth diode segment 244.

In some embodiments, the first electrical conductor 229, the thirdelectrical conductor 233, and the fifth electrical conductor 237 areformed as respective parts of a common electrical conductor that extendscontinuously across the first diode segment 241, the second diodesegment 242, the third diode segment 243, and the fourth diode segment244 at a location over the first cladding region 102 on the first sideof the core region 103. In some embodiments, the second electricalconductor 231, the fourth electrical conductor 235, and the sixthelectrical conductor 239 are formed as respective parts of anothercommon electrical conductor that extends continuously across the firstdiode segment 241, the second diode segment 242, the third diode segment243, and the fourth diode segment 244 at a location over the secondcladding region 104 on the second side of the core region 103.

The first diode of the first diode segment 241 is configured as a firstPIN diode across the optical waveguide 200. The first diode segment 241includes an N-doped region 213 formed within an outer section of thefirst cladding region 102, a P-doped region 215 formed within an outersection of the second cladding region 104, and an intrinsic region 214between the N-doped region 213 and the P-doped region 215. The built-involtage of the first diode of the first diode segment 241 provided bythe N-doped region 213 and the P-doped region 215 establishes the firstintrinsic electric field E1 across the first diode segment 241, andparticularly across the core region 103 within the first diode segment241. In some embodiments, the intrinsic region 214 includes an entiretyof the core region 103 within the first diode segment 241, a portion ofthe first cladding region 102 within the first diode segment 241, and aportion of the second cladding region 104 within the first diode segment241. It should be understood that the core region 103 is present in theintrinsic region 214 where the first intrinsic electric field E1 ishigh. The width of the intrinsic region 214 is created wide enough so asto avoid overlap of the N-doped region 213 and the P-doped region 215within the optical waveguide 200. The N-doped region 213, the P-dopedregion 215, and the intrinsic region 214 extend along a full length ofthe core region 103 within the first diode segment 241.

The second diode of the second diode segment 242 is configured as asecond PIN diode across the optical waveguide 200. The second diodesegment 242 includes a P-doped region 217 formed within an outer sectionof the first cladding region 102, an N-doped region 219 formed within anouter section of the second cladding region 104, and an intrinsic region218 between the P-doped region 217 and the N-doped region 219. Thebuilt-in voltage of the second diode of the second diode segment 242provided by the P-doped region 217 and the N-doped region 219 establishthe second intrinsic electric field E2 across the second diode segment242, and particularly across the core region 103 within the second diodesegment 242. In some embodiments, the intrinsic region 218 includes anentirety of the core region 103 within the second diode segment 242, aportion of the first cladding region 102 within the second diode segment242, and a portion of the second cladding region 104 within the seconddiode segment 242. It should be understood that the core region 103 ispresent in the intrinsic region 218 where the second intrinsic electricfield E2 is high. The width of the intrinsic region 218 is created wideenough so as to avoid overlap of the P-doped region 217 and the N-dopedregion 219 within the optical waveguide 200. The P-doped region 217, theN-doped region 219, and the intrinsic region 218 extend along a fulllength of the core region 103 within the second diode segment 242. Itshould be understood that the second diode of the second diode segment242 has a reversed orientation with respect to the first diode of thefirst diode segment 241, such that the second intrinsic electric fieldE2 has a reversed orientation with respect to the first intrinsicelectric field E1, as indicated by directions 252 and 251.

The third diode of the third diode segment 243 is configured as a thirdPIN diode across the optical waveguide 200. The third diode segment 243includes an N-doped region 221 formed within an outer section of thefirst cladding region 102, a P-doped region 223 formed within an outersection of the second cladding region 104, and an intrinsic region 222between the N-doped region 221 and the P-doped region 223. The built-involtage of the third diode of the third diode segment 243 provided bythe N-doped region 221 and the P-doped region 223 establish the thirdintrinsic electric field E3 across the third diode segment 243, andparticularly across the core region 103 within the third diode segment243. In some embodiments, the intrinsic region 222 includes an entiretyof the core region 103 within the third diode segment 243, a portion ofthe first cladding region 102 within the third diode segment 243, and aportion of the second cladding region 104 within the third diode segment243. It should be understood that the core region 103 is present in theintrinsic region 222 where the third intrinsic electric field E3 ishigh. The width of the intrinsic region 222 is created wide enough so asto avoid overlap of the N-doped region 221 and the P-doped region 223within the optical waveguide 200. The N-doped region 221, the P-dopedregion 223, and the intrinsic region 222 extend along a full length ofthe core region 103 within the third diode segment 243. It should beunderstood that the third diode of the third diode segment 243 has areversed orientation with respect to the second diode of the seconddiode segment 242, such that the third intrinsic electric field E3 has areversed orientation with respect to the second intrinsic electric fieldE2, as indicated by directions 253 and 252.

The fourth diode of the fourth diode segment 244 is configured as afourth PIN diode across the optical waveguide 200. The fourth segment244 includes a P-doped region 225 formed within an outer section of thefirst cladding region 102, an N-doped region 227 formed within an outersection of the second cladding region 104, and an intrinsic region 226between the P-doped region 225 and the N-doped region 227. The built-involtage of the fourth diode of the fourth diode segment 244 provided bythe P-doped region 225 and the N-doped region 227 establish the fourthintrinsic electric field E4 across the fourth diode segment 244, andparticularly across the core region 103 within the fourth diode segment244. In some embodiments, the intrinsic region 226 includes an entiretyof the core region 103 within the fourth diode segment 244, a portion ofthe first cladding region 102 within the fourth diode segment 244, and aportion of the second cladding region 104 within the fourth diodesegment 244. It should be understood that the core region 103 is presentin the intrinsic region 226 where the fourth intrinsic electric field E4is high. The width of the intrinsic region 226 is created wide enough soas to avoid overlap of the P-doped region 225 and the N-doped region 227within the optical waveguide 200. The P-doped region 225, the N-dopedregion 227, and the intrinsic region 226 extend along a full length ofthe core region 103 within the fourth diode segment 244. It should beunderstood that the fourth diode of the fourth diode segment 244 has areversed orientation with respect to the third diode of the third diodesegment 243, such that the fourth intrinsic electric field E4 has areversed orientation with respect to the third intrinsic electric fieldE3, as indicated by directions 254 and 253.

It should be understood that the first diode segment 241 and the thirddiode segment 243 are configured in the same way. Also, the second diodesegment 242 and the fourth diode segment 244 are configured in the sameway. In this manner, the configurations of the first diode segment 241and the second diode segment 242 repeat in a sequential manner along thelength of the optical waveguide 200, including along the length of theoptical waveguide 200 that is not explicitly shown in FIG. 2A. Thus, theoptical waveguide 200 includes repeated instances of the first diodesegment 241 and the second diode segment 242 along the length of theoptical waveguide 200. It should be understood that the first diodesegment 241, the second diode segment 242, the third diode segment 243,and the fourth diode segment 244 are shown in FIG. 2A for descriptivepurposes, but the optical waveguide 200 is not limited to four diodesegments of alternating orientation. In various embodiments, the opticalwaveguide 200 includes many instances of the configuration of the firstdiode segment 241 and the configuration of the second diode segment 242repeated in an alternating manner along the length of the opticalwaveguide 200. In some embodiments, neighboring diode segments (241/242,242/243, 243/244, etc.) of alternate orientation are contiguous witheach other in the lengthwise direction of the optical waveguide 200. Forexample, the second diode segment 242 is contiguous with the first diodesegment 241 in the lengthwise direction of the optical waveguide 200,such that the P-doped region 217 is contiguous with the N-doped region213, and such that the N-doped region 219 is contiguous with the P-dopedregion 215. Also, the third diode segment 243 is contiguous with thesecond diode segment 242 in the lengthwise direction of the opticalwaveguide 200, such that the N-doped region 221 is contiguous with theP-doped region 217, and such that the P-doped region 223 is contiguouswith the N-doped region 219. Also, the fourth diode segment 244 iscontiguous with the third diode segment 243 in the lengthwise directionof the optical waveguide 200, such that the P-doped region 225 iscontiguous with the N-doped region 221, and such that the N-doped region227 is contiguous with the P-doped region 223.

In some embodiments, each of the first electrical conductor 229, thesecond electrical conductor 231, the third electrical conductor 233, thefourth electrical conductor 235, the fifth electrical conductor 237, andthe sixth electrical conductor 239 is formed from material(s) used toform low-resistance electrical contacts in silicon. In some embodiments,each of the first electrical conductor 229, the second electricalconductor 231, the third electrical conductor 233, the fourth electricalconductor 235, the fifth electrical conductor 237, and the sixthelectrical conductor 239 is formed substantially outside of the opticalwaveguide 200. In some embodiments, each of the first electricalconductor 229, the second electrical conductor 231, the third electricalconductor 233, the fourth electrical conductor 235, the fifth electricalconductor 237, and the sixth electrical conductor 239 is formed tosubstantially overlap each of the doped regions to which it iselectrically connected. In some embodiments, the first electricalconductor 229, the third electrical conductor 233, and the fifthelectrical conductor 237 are replaced by a layer of silicide thatextends continuously over the N-doped region 213, the P-doped region217, the N-doped region 221, and the P-doped region 225. Similarly, insome embodiments, the second electrical conductor 231, the fourthelectrical conductor 235, and the sixth electrical conductor 239 arereplaced by a layer of silicide that extends continuously over theP-doped region 215, the N-doped region 219, the P-doped region 223, andthe N-doped region 227.

FIG. 2D shows the top view of the optical waveguide 200 of FIG. 2A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region 103 by the diodes of the first diodesegment 241, the second diode segment 242, the third diode segment 243,and the fourth diode segment 244, in accordance with some embodiments.The first intrinsic electric field E1 in the first diode segment 241pulls the free-carrier electrons (e) out of the core region 103 to theN-doped region 213, and pulls the free-carrier holes (h) out of the coreregion 103 to the P-doped region 215. The second intrinsic electricfield E2 in the second diode segment 242 pulls the free-carrierelectrons (e) out of the core region 103 to the N-doped region 219, andpulls the free-carrier holes (h) out of the core region 103 to theP-doped region 217. The third intrinsic electric field E3 in the thirddiode segment 243 pulls the free-carrier electrons (e) out of the coreregion 103 to the N-doped region 221, and pulls the free-carrier holes(h) out of the core region 103 to the P-doped region 223. The fourthintrinsic electric field E4 in the fourth diode segment 244 pulls thefree-carrier electrons (e) out of the core region 103 to the N-dopedregion 227, and pulls the free-carrier holes (h) out of the core region103 to the P-doped region 225. The first electrical conductor 229 andthe second electrical conductor 231 facilitate completion of anelectrical circuit between the first diode segment 241 and the seconddiode segment 242. The second electrical conductor 233 and the thirdelectrical conductor 235 facilitate completion of an electrical circuitbetween the second diode segment 242 and the third diode segment 243.The fifth electrical conductor 237 and the sixth electrical conductor239 facilitate completion of an electrical circuit between the thirddiode segment 243 and the fourth diode segment 244.

The intrinsic electric fields E1-E4 across the optical waveguide 200sweep out free-carriers that are generated within the core region 103 byTPA. By removing these free-carriers from the core region 103, thefree-carrier concentration in the core region 103 stays low, whichminimizes optical losses within the core region 103 due to free-carrierabsorption. The orientations (perpendicular to the lengthwise centerline106 of the optical waveguide 200) of the first, second, third, andfourth diode segments 241, 242, 243, 244, respectively, are alternatedso as to close the electrical current loops created by the free-carriersweep-out from the core region 103. It should be understood that withoutalternating the orientations of neighboring ones of the first, second,third, and fourth diode segments 241, 242, 243, 244, respectively, theelectrical current generated by the sweep-out of TPA-generatedfree-carriers from the core region 103 would create an electrical chargebuild-up at the sides of the optical waveguide 200 that would counteractthe built-in voltages of the first, second, third, and fourth diodesegments 241, 242, 243, 244, respectively, and correspondinglyshutdown/prevent free-carrier sweep-out from the core region 103.Therefore, by alternating the orientations of the first, second, third,and fourth diode segments 241, 242, 243, 244, respectively, along thelength of the optical waveguide 200, the electrical current generated byfree-carrier sweep-out in a given one of the diode segments 241, 242,243, 244 is balanced by the electrical current generated in neighboringdiode segments.

For example, in the example of FIG. 2D, the electrical current generatedby free-carrier sweep-out in the first diode segment 241 is balanced bythe electrical current generated by free-carrier sweep-out in the seconddiode segment 242. The first electrical conductor 229 and the secondelectrical conductor 231 facilitate balancing of electrical currentsbetween the first diode segment 241 and the second diode segment 242.Also, the electrical current generated by free-carrier sweep-out in thesecond diode segment 242 is balanced by the electrical current generatedby free-carrier sweep-out in the first diode segment 241 and the thirddiode segment 243. The third electrical conductor 233 and the fourthelectrical conductor 235 facilitate balancing of electrical currentsbetween the second diode segment 242 and the third diode segment 243.Also, the electrical current generated by free-carrier sweep-out in thethird diode segment 243 is balanced by the electrical current generatedby free-carrier sweep-out in the second diode segment 242 and the fourthdiode segment 244. The fifth electrical conductor 237 and the sixthelectrical conductor 239 facilitate balancing of electrical currentsbetween the third diode segment 243 and the fourth diode segment 244.Also, the electrical current generated by free-carrier sweep-out in thefourth diode segment 244 is balanced by the electrical current generatedby free-carrier sweep-out in the third diode segment 243.

FIG. 2E shows a curved portion of the optical waveguide 200, inaccordance with some embodiments. FIG. 2F shows a vertical cross-sectionview through the optical waveguide 200, referenced as View C-C in FIG.2E, in accordance with some embodiments. In some embodiments, the curvedportion of the optical waveguide 200 has the full-thickness 121 coreregion 103, the partial-thickness 115 first inner cladding region 105,the partial-thickness 119 second inner cladding region 107, thefull-thickness 113 first outer cladding region 109, and thefull-thickness 117 second outer cladding region 111. Alternatively, insome embodiments of the curved portion of the optical waveguide 200, thethickness 113 of the first outer cladding region 109 is substantiallyequal to the partial-thickness 115 of the first inner cladding region105. Also, in some embodiments of the curved portion of the opticalwaveguide 200, the thickness 117 of the second outer cladding region 111is substantially equal to the partial-thickness 119 of the second innercladding region 107.

The example of FIG. 2E shows diode segments 261-267. The orientations ofthe diode segments 261-267 across the optical waveguide 200 arealternated along the curved portion of the optical waveguide 200. Insome embodiments, the lengthwise centerline 106 of the optical waveguide200 has a radius of curvature 291 about a point 290. In this manner, aninner side 298 of the curved portion of the optical waveguide 200 has asmaller radius of curvature about the point 290 than a correspondingouter side 299 of the curved portion of the optical waveguide 200 at agiven position along the lengthwise centerline 106 of the opticalwaveguide 200.

In some embodiments, a continuous electrical conductor 295 is formed onthe first outer cladding region 109 along the inner side 298 of thecurved portion of the optical waveguide 200. Also, in some embodiments,a continuous electrical conductor 296 is formed on the second outercladding region 111 along the outer side 299 of the curved portion ofthe optical waveguide 200. In some embodiments, the continuouselectrical conductors 295 and 296 are formed as respective silicideregions. In some embodiments, the continuous electrical conductors 295and 296 are formed as respective electrically conductive structuresdisposed in electrical contact with the optical waveguide 200. In someembodiments, rather than having the continuous electrical conductors 295and 296, the curved portion of the optical waveguide 200 is formed tohave discrete electrical conductors respectively disposed to connectneighboring N-doped and P-doped regions of the optical waveguide 200,such as previously described with regard to the electrical conductors229, 231, 233, 235, 237, and 239.

The diode segment 261 includes an N-doped region 271, a P-doped region273, and an intrinsic region 272 extending between the N-doped region271 and the P-doped region 273. The diode segment 261 has an intrinsic(built-in) electrical field E5 that extends across the core region 103from the N-doped region 271 to the P-doped region 273. The diode segment261 is contiguous with the diode segment 244, such that the N-dopedregion 271 is contiguous with the P-doped region 225, and such that theP-doped region 273 is contiguous with the N-doped region 227, and suchthat the intrinsic region 272 is contiguous with the intrinsic region226.

The next diode segment 262 includes a P-doped region 274, an N-dopedregion 276, and an intrinsic region 275 extending between the P-dopedregion 274 and the N-doped region 276. The diode segment 262 has anintrinsic (built-in) electrical field E6 that extends across the coreregion 103 from the N-doped region 276 to the P-doped region 274. Thediode segment 262 is contiguous with the diode segment 261, such thatthe P-doped region 274 is contiguous with the N-doped region 271, andsuch that the N-doped region 276 is contiguous with the P-doped region273, and such that the intrinsic region 275 is contiguous with theintrinsic region 272.

The next diode segment 263 includes an N-doped region 277, a P-dopedregion 279, and an intrinsic region 278 extending between the N-dopedregion 277 and the P-doped region 279. The diode segment 263 has anintrinsic (built-in) electrical field E7 that extends across the coreregion 103 from the N-doped region 277 to the P-doped region 279. Thediode segment 263 is contiguous with the diode segment 262, such thatthe N-doped region 277 is contiguous with the P-doped region 274, andsuch that the P-doped region 279 is contiguous with the N-doped region276, and such that the intrinsic region 278 is contiguous with theintrinsic region 275.

The next diode segment 264 includes a P-doped region 280, an N-dopedregion 282, and an intrinsic region 281 extending between the P-dopedregion 280 and the N-doped region 282. The diode segment 264 has anintrinsic (built-in) electrical field E8 that extends across the coreregion 103 from the N-doped region 282 to the P-doped region 280. Thediode segment 264 is contiguous with the diode segment 263, such thatthe P-doped region 280 is contiguous with the N-doped region 277, andsuch that the N-doped region 282 is contiguous with the P-doped region279, and such that the intrinsic region 281 is contiguous with theintrinsic region 278.

The next diode segment 265 includes an N-doped region 283, a P-dopedregion 285, and an intrinsic region 284 extending between the N-dopedregion 283 and the P-doped region 285. The diode segment 265 has anintrinsic (built-in) electrical field E9 that extends across the coreregion 103 from the N-doped region 283 to the P-doped region 285. Thediode segment 265 is contiguous with the diode segment 264, such thatthe N-doped region 283 is contiguous with the P-doped region 280, andsuch that the P-doped region 285 is contiguous with the N-doped region282, and such that the intrinsic region 284 is contiguous with theintrinsic region 281.

The next diode segment 266 includes a P-doped region 286, an N-dopedregion 288, and an intrinsic region 287 extending between the P-dopedregion 286 and the N-doped region 288. The diode segment 266 has anintrinsic (built-in) electrical field E10 that extends across the coreregion 103 from the N-doped region 288 to the P-doped region 286. Thediode segment 266 is contiguous with the diode segment 265, such thatthe P-doped region 286 is contiguous with the N-doped region 283, andsuch that the N-doped region 288 is contiguous with the P-doped region285, and such that the intrinsic region 287 is contiguous with theintrinsic region 284.

The next diode segment 267 includes an N-doped region 289, a P-dopedregion 291, and an intrinsic region 290 extending between the N-dopedregion 289 and the P-doped region 291. The diode segment 267 has anintrinsic (built-in) electrical field E11 that extends across the coreregion 103 from the N-doped region 289 to the P-doped region 291. Thediode segment 267 is contiguous with the diode segment 266, such thatthe N-doped region 289 is contiguous with the P-doped region 286, andsuch that the P-doped region 291 is contiguous with the N-doped region288, and such that the intrinsic region 290 is contiguous with theintrinsic region 287.

FIG. 2G shows plots of optical angular propagation constant as afunction the radius of curvature 291 of the lengthwise centerline 106 ofthe optical waveguide 200 about the point 290 for the primary opticalmode within the core region 103 and the primary optical mode in thesecond outer cladding region 111 for various widths (300 nanometers(nm), 200 nm, 150 nm) of the second outer cladding region 111, inaccordance with some embodiments. The width 118 of the second outercladding region 111 is depicted in FIG. 2F. FIG. 2G shows that theoptical angular propagation constant of the primary optical mode withinthe second outer cladding region 111 decreases as the width 118 of thesecond outer cladding region 111 decreases, and vice-versa. The 300 nmwide outer cladding region curve in FIG. 2G shows that the opticalangular propagation constant of the primary optical mode within thesecond outer cladding region 111 substantially matches the opticalangular propagation constant of the primary optical mode within the coreregion 103 at a particular combination of radius of curvature 291 of theoptical waveguide 200 and width 118 of the second outer cladding region111. In some embodiments, the width 118 of the second outer claddingregion 111 is set small enough to avoid optical phase-matchingresonances between light guided in the primary optical mode of the coreregion 103 and optical modes of the second outer cladding region 111.The optical phase-matching resonance condition takes into account theradius of curvature 291 of the lengthwise centerline 106 of the opticalwaveguide 200, which effectively increases the effective optical indexof refraction of the optical modes of the second outer cladding region111. In some embodiments, the optical phase-matching resonance conditionis determined in terms of optical angular propagation constant. In someembodiments in which the curved portion of the optical waveguide 200 hasboth the first outer cladding region 109 on the inside of the curve andthe second outer cladding region 111 on the outside of the curve, theeffective optical index of refraction corrections will be opposite forthe first outer cladding region 109 and the second outer cladding region111.

The alternating orientations of the diode segments (241-244 and 261-267,etc.) along the length of the optical waveguide 200 avoids the need forhaving additional electrical interconnection structures around theoptical waveguide 200. In the optical waveguide 200, the electricalfield used to sweep out free-carriers from the core region 103 is theintrinsic (built-in) electrical field of the diode junctions within eachof the diode segments (241-244 and 261-267, etc.). In some embodiments,because the electrical current generated by TPA within the core region103 results in a voltage drop across the optical waveguide 200, whichwould tend to counter the free-carrier sweep-out effect, the respectivelengths of the diode segments (241-244 and 261-267, etc.) along theoptical waveguide 200 are made smaller to enhance the electrical currentbalancing between neighboring ones of the diode segments (241-244 and261-267, etc.) having opposite orientations across the optical waveguide200. Also, in some embodiments, some of the different diode segments(241-244 and 261-267, etc.) along the optical waveguide 200 havedifferent lengths, as measured along the lengthwise centerline 106 ofthe optical waveguide 200. In some embodiments, the different lengths ofthe different diode segments (241-244 and 261-267, etc.) along theoptical waveguide 200 are defined to compensate for an electricalcurrent density imbalance between the different diode segments (241-244and 261-267, etc.).

In some embodiments, optical decay along the optical waveguide 200 willaffect the TPA electrical current generation and create an electricalcurrent imbalance which will result in a small voltage drop across theoptical waveguide 200 between the first cladding region 102 and thesecond cladding region 104. In some embodiments, the lengths of thedifferent diode segments (241-244 and 261-267, etc.) along the opticalwaveguide 200 are defined to compensate for the electrical currentdensity differences (imbalances) along the optical waveguide 200 causedby the optical decay effect on TPA electrical current generation.Therefore, in some embodiments, the lengths of the different diodesegments (241-244 and 261-267, etc.) along the optical waveguide 200 aredefined to improve electrical current balance along the length of theoptical waveguide 200, which provides for reduction in voltage build-upbetween the first cladding region 102 and the second cladding region 104along the length of the optical waveguide 200.

It should be understood that, in some embodiments, the optical waveguide200 provides a silicon optical waveguide structure having reducedTPA-driven optical power loss at high optical power. As described withregard to FIGS. 2A-2F, in some embodiments, the optical waveguide 200 isa rib-shaped optical waveguide structure that is doped on each side tocreate multiple diode structures of alternating orientation along thelength of the optical waveguide 200. Also, it should be understood that,in some embodiments, the optical waveguide 200 is constructed withminimal to no additional electrical interconnection structures near oron the optical waveguide 200, which is beneficial at least because suchadditional electrical interconnection structures could potentiallyoptically interfere with light traveling through the optical waveguide200. In particular, in some embodiments, the optical waveguide 200 doesnot require routing of metal traces over the core region 103 in order toshort the diode terminals of the diode segments (241-244 and 261-267,etc.) along the length of the optical waveguide 200. In someembodiments, each of the diode segments (241-244 and 261-267, etc.) ofthe optical waveguide 200 is not connected to any electrical circuitexternal to the optical waveguide 200.

FIG. 3 shows simulation results of free-carrier build-up in the coreregion 103 at different optical powers for various embodiments of theoptical waveguide 200 in which the width of the intrinsic regions 214,218, 222, 226 is modified, in accordance with some embodiments. Morespecifically, FIG. 3 shows the average hole concentration in the coreregion 103 as a function of the optical power of the light transmittedthrough the optical waveguide 200. A curve 401 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 2 micrometers. A curve 402 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 1.8 micrometers. A curve 403 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 1.6 micrometers. A curve 404 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 1.4 micrometers. A curve 405 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 1.2 micrometers. A curve 406 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 1.0 micrometers. A curve 407 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 0.8 micrometers. A curve 408 shows the average holeconcentration in the core region 103 as a function of optical power forthe optical waveguide 200 in which the width (as measured perpendicularto the lengthwise centerline 106) of each of the intrinsic regions 214,218, 222, 226 is 0.6 micrometers. Curves 401 through 408 show that asthe width of the intrinsic regions 214, 218, 222, 226 is reduced in theoptical waveguide 200, the concentration of free-carriers within thecore region 103 is correspondingly reduced.

FIG. 3 also shows a curve 409 for the average hole concentration in thecore region 103 as a function of optical power for the undoped opticalwaveguide 100 of FIG. 1A that does not include the diode segments 241,242, 243, 244, etc., such as present within the optical waveguide 200.FIG. 3 also shows a curve 410 for the average hole concentration as afunction of optical power within an undoped strip optical waveguide inwhich the strip optical waveguide has a substantially uniform verticalthickness along its length. The strip optical waveguide associated withcurve 410 is like the optical waveguide 100 of FIG. 1A, except withsubstantially equal sizes for each of the thickness 113 of the firstouter cladding region 109, the thickness 115 of the first inner claddingregion 105, the thickness 121 of the core region 103, the thickness 119of the second inner cladding region 107, and the thickness 117 of thesecond outer cladding region 111. FIG. 3 shows that the opticalwaveguide 200 has about a three order of magnitude reduction infree-carrier concentration in the core region 103 at about 30 milliWattsas compared with the strip optical waveguide.

FIG. 4A shows a top view of an optical waveguide 300, in accordance withsome embodiments. FIG. 4B shows a vertical cross-section view throughthe optical waveguide 300, referenced as View A-A in FIG. 4A, inaccordance with some embodiments. FIG. 4C shows a vertical cross-sectionview through the optical waveguide 300, referenced as View B-B in FIG.4A, in accordance with some embodiments. The optical waveguide 400 is amodification of the optical waveguide 100 of FIGS. 1A-1B. The opticalwaveguide 300 includes the core region 103, the first cladding region102, and the second cladding region 104 as described with regard toFIGS. 1A-1B. The optical waveguide 300 includes a first diode segment341, a second diode segment 342, a third diode segment 343, and a fourthdiode segment 344. Each of the first diode segment 341, the second diodesegment 342, the third diode segment 343, and the fourth diode segment344 includes respective portions of the core region 103, the firstcladding region 102, and the second cladding region 104. In someembodiments, the second diode segment 342 is contiguous with both thefirst diode segment 341 and the third diode segment 343, and the fourthdiode segment 344 is contiguous with the third diode segment 343. Itshould be understood that for ease of description FIG. 4A depicts aportion of the optical waveguide 300. The pattern of the configurationsof the first diode segment 341, the second diode segment 342, the thirddiode segment 343, and the fourth diode segment 344 continues along thelength of the optical waveguide 300. Therefore, in various embodiments,the optical waveguide 300 includes many more than just the four diodesegments 341, 342, 343, and 344.

The first diode segment 341 is configured to form a first PN diodeacross the optical waveguide 300 such that a first intrinsic electricfield E1 extends across the first diode segment 341 in a first direction351 substantially perpendicular to the lengthwise centerline 106 of theoptical waveguide 300. The first diode segment 341 includes a firstN-doped region 313 formed across the first half of the optical waveguide300 and a first P-doped region 315 formed across the second half of theoptical waveguide 300. The first N-doped region 313 extends across thefirst cladding region 102 outward from the lengthwise centerline 106 ofthe optical waveguide 300. The first P-doped region 315 extends acrossthe second cladding region 104 outward from the lengthwise centerline106 of the optical waveguide 300. A first depletion region 314 existswithin the first diode segment 341 along an interface between the firstN-doped region 313 and the first P-doped region 315. The first N-dopedregion 313, the first P-doped region 315, and the associated firstdepletion region 314 extend along a full length of the core region 103within the first diode segment 341.

The built-in voltage of the first PN diode of the first diode segment341 provided by the first N-doped region 313 and the first P-dopedregion 315 establishes the first intrinsic electric field E1 across thefirst diode segment 341, and particularly across the core region 103within the first diode segment 341. In some embodiments, the firstdepletion region 314 includes an entirety of the core region 103 withinthe first diode segment 341, a portion of the first cladding region 102within the first diode segment 341, and a portion of the second claddingregion 104 within the first diode segment 341. It should be understoodthat the core region 103 is present in the first depletion region 314where the first intrinsic electric field E1 is high. In someembodiments, the respective doping levels of the first N-doped region313 and the first P-doped region 315 are sufficiently low to provide thefirst depletion region 314 with a sufficiently large width to encompassthe core region 103 within the first diode segment 341, andcorrespondingly reduce optical losses caused by overlap of the coreregion 103 with the first N-doped region 313 and the first P-dopedregion 315.

The second diode segment 342 is configured to form a second PN diodeacross the optical waveguide 300 such that a second intrinsic electricfield E2 extends across the second diode segment 342 in a seconddirection 352 substantially perpendicular to the lengthwise centerline106 of the optical waveguide 300. The second diode segment 342 includesa second P-doped region 317 formed across the first half of the opticalwaveguide 300 and a second N-doped region 319 formed across the secondhalf of the optical waveguide 300. The second P-doped region 317 extendsacross the first cladding region 102 outward from the lengthwisecenterline 106 of the optical waveguide 300. The second N-doped region319 extends across the second cladding region 104 outward from thelengthwise centerline 106 of the optical waveguide 300. A seconddepletion region 318 exists within the second diode segment 342 along aninterface between the second P-doped region 317 and the second N-dopedregion 319. The second P-doped region 317, the second N-doped region319, and the associated second depletion region 318 extend along a fulllength of the core region 103 within the second diode segment 342.

The built-in voltage of the second PN diode of the second diode segment342 provided by the second P-doped region 317 and the second N-dopedregion 319 establishes the second intrinsic electric field E2 across thesecond diode segment 342, and particularly across the core region 103within the second diode segment 342. In some embodiments, the seconddepletion region 318 includes an entirety of the core region 103 withinthe second diode segment 342, a portion of the first cladding region 102within the second diode segment 342, and a portion of the secondcladding region 104 within the second diode segment 342. It should beunderstood that the core region 103 is present in the second depletionregion 318 where the second intrinsic electric field E2 is high. In someembodiments, the respective doping levels of the second P-doped region317 and the second N-doped region 319 are sufficiently low to providethe second depletion region 318 with a sufficiently large width toencompass the core region 103 within the second diode segment 342, andcorrespondingly reduce optical losses caused by overlap of the coreregion 103 with the second P-doped region 317 and the second N-dopedregion 319. It should be understood that the second PN diode of thesecond diode segment 342 has a reversed orientation with respect to thefirst PN diode of the first diode segment 341, such that the secondintrinsic electric field E2 has a reversed orientation with respect tothe first intrinsic electric field E1, as indicated by directions 352and 351.

The third diode segment 343 is configured to form a third PN diodeacross the optical waveguide 300 such that a third intrinsic electricfield E3 extends across the third diode segment 343 in a third direction353 substantially perpendicular to the lengthwise centerline 106 of theoptical waveguide 300. The third diode segment 343 includes a thirdN-doped region 321 formed across the first half of the optical waveguide300 and a third P-doped region 323 formed across the second half of theoptical waveguide 300. The third N-doped region 321 extends across thefirst cladding region 102 outward from the lengthwise centerline 106 ofthe optical waveguide 300. The third P-doped region 323 extends acrossthe second cladding region 104 outward from the lengthwise centerline106 of the optical waveguide 300. A third depletion region 322 existswithin the third diode segment 343 along an interface between the thirdN-doped region 321 and the third P-doped region 323. The third N-dopedregion 321, the third P-doped region 323, and the associated thirddepletion region 322 extend along a full length of the core region 103within the third diode segment 343.

The built-in voltage of the third PN diode of the third diode segment343 provided by the third N-doped region 321 and the third P-dopedregion 323 establishes the third intrinsic electric field E3 across thethird diode segment 343, and particularly across the core region 103within the third diode segment 343. In some embodiments, the thirddepletion region 322 includes an entirety of the core region 103 withinthe third diode segment 343, a portion of the first cladding region 102within the third diode segment 343, and a portion of the second claddingregion 104 within the third diode segment 343. It should be understoodthat the core region 103 is present in the third depletion region 322where the third intrinsic electric field E3 is high. In someembodiments, the respective doping levels of the third N-doped region321 and the third P-doped region 323 are sufficiently low to provide thethird depletion region 322 with a sufficiently large width to encompassthe core region 103 within the third diode segment 343, andcorrespondingly reduce optical losses caused by overlap of the coreregion 103 with the third N-doped region 321 and the third P-dopedregion 323. It should be understood that the third PN diode of the thirddiode segment 343 has a reversed orientation with respect to the secondPN diode of the second diode segment 342, such that the third intrinsicelectric field E3 has a reversed orientation with respect to the secondintrinsic electric field E2, as indicated by directions 353 and 352.

The fourth diode segment 344 is configured to form a fourth PN diodeacross the optical waveguide 300 such that a fourth intrinsic electricfield E4 extends across the fourth diode segment 344 in a fourthdirection 354 substantially perpendicular to the lengthwise centerline106 of the optical waveguide 300. The fourth diode segment 344 includesa fourth P-doped region 325 formed across the first half of the opticalwaveguide 300 and a fourth N-doped region 327 formed across the secondhalf of the optical waveguide 300. The fourth P-doped region 325 extendsacross the first cladding region 102 outward from the lengthwisecenterline 106 of the optical waveguide 300. The fourth N-doped region327 extends across the second cladding region 104 outward from thelengthwise centerline 106 of the optical waveguide 300. A fourthdepletion region 326 exists within the fourth diode segment 344 along aninterface between the fourth P-doped region 325 and the fourth N-dopedregion 327. The fourth P-doped region 325, the fourth N-doped region327, and the associated fourth depletion region 326 extend along a fulllength of the core region 103 within the fourth diode segment 344.

The built-in voltage of the fourth PN diode of the fourth diode segment344 provided by the fourth P-doped region 325 and the fourth N-dopedregion 327 establishes the fourth intrinsic electric field E4 across thefourth diode segment 344, and particularly across the core region 103within the fourth diode segment 344. In some embodiments, the fourthdepletion region 326 includes an entirety of the core region 103 withinthe fourth diode segment 344, a portion of the first cladding region 102within the fourth diode segment 344, and a portion of the secondcladding region 104 within the fourth diode segment 344. It should beunderstood that the core region 103 is present in the fourth depletionregion 326 where the fourth intrinsic electric field E4 is high. In someembodiments, the respective doping levels of the fourth P-doped region325 and the fourth N-doped region 327 are sufficiently low to providethe fourth depletion region 326 with a sufficiently large width toencompass the core region 103 within the fourth diode segment 344, andcorrespondingly reduce optical losses caused by overlap of the coreregion 103 with the fourth P-doped region 325 and the fourth N-dopedregion 327. It should be understood that the fourth PN diode of thefourth diode segment 344 has a reversed orientation with respect to thethird PN diode of the third diode segment 343, such that the fourthintrinsic electric field E4 has a reversed orientation with respect tothe third intrinsic electric field E3, as indicated by directions 354and 353.

In some embodiments, a first electrical conductor 329 is disposed toelectrically connect the first diode segment 341 and the second diodesegment 342 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a secondelectrical conductor 331 is disposed to electrically connect the firstdiode segment 341 and the second diode segment 342 at a location overthe second cladding region 104 on the second side of the core region103. In some embodiments, the first electrical conductor 329 is formedas a region of silicide, and the second electrical conductor 331 isformed as another region of silicide. In some embodiments, the firstelectrical conductor 329 is formed as an electrically conductivestructure disposed on both a region of the first diode segment 341 and aregion of the second diode segment 342, and the second electricalconductor 331 is formed as an electrically conductive structure disposedon both a region of the first diode segment 341 and a region of thesecond diode segment 342.

In some embodiments, a third electrical conductor 333 is disposed toelectrically connect the second diode segment 342 and the third diodesegment 343 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a fourthelectrical conductor 335 is disposed to electrically connect the seconddiode segment 342 and the third diode segment 343 at a location over thesecond cladding region 104 on the second side of the core region 103. Insome embodiments, the third electrical conductor 333 is formed as aregion of silicide, and the fourth electrical conductor 335 is formed asanother region of silicide. In some embodiments, the third electricalconductor 333 is formed as an electrically conductive structure disposedon both a region of the second diode segment 342 and a region of thethird diode segment 343, and the fourth electrical conductor 335 isformed as an electrically conductive structure disposed on both a regionof the second diode segment 342 and a region of the third diode segment343.

In some embodiments, a fifth electrical conductor 337 is disposed toelectrically connect the third diode segment 343 and the fourth diodesegment 344 at a location over the first cladding region 102 on thefirst side of the core region 103. Also, in some embodiments, a sixthelectrical conductor 339 is disposed to electrically connect the thirddiode segment 343 and the fourth diode segment 344 at a location overthe second cladding region 104 on the second side of the core region103. In some embodiments, the fifth electrical conductor 337 is formedas a region of silicide, and the sixth electrical conductor 339 isformed as another region of silicide. In some embodiments, the fifthelectrical conductor 337 is formed as an electrically conductivestructure disposed on both a region of the third diode segment 343 and aregion of the fourth diode segment 344, and the sixth electricalconductor 339 is formed as an electrically conductive structure disposedon both a region of the third diode segment 343 and a region of thefourth diode segment 344.

In some embodiments, the first electrical conductor 329, the thirdelectrical conductor 333, and the fifth electrical conductor 337 areformed as respective parts of a common electrical conductor that extendscontinuously across the first diode segment 341, the second diodesegment 342, the third diode segment 343, and the fourth diode segment344 at a location over the first cladding region 102 on the first sideof the core region 103. In some embodiments, the second electricalconductor 331, the fourth electrical conductor 335, and the sixthelectrical conductor 339 are formed as respective parts of anothercommon electrical conductor that extends continuously across the firstdiode segment 341, the second diode segment 342, the third diode segment343, and the fourth diode segment 344 at a location over the secondcladding region 104 on the second side of the core region 103.

It should be understood that the first diode segment 341 and the thirddiode segment 343 are configured in the same way. Also, the second diodesegment 342 and the fourth diode segment 344 are configured in the sameway. In this manner, the configurations of the first diode segment 341and the second diode segment 342 repeat in a sequential manner along thelength of the optical waveguide 300, including along the length of theoptical waveguide 300 that is not explicitly shown in FIG. 4A. Thus, theoptical waveguide 300 includes repeated instances of the first diodesegment 341 and the second diode segment 342 along the length of theoptical waveguide 300. It should be understood that the first diodesegment 341, the second diode segment 342, the third diode segment 343,and the fourth diode segment 344 are shown in FIG. 4A for descriptivepurposes, but the optical waveguide 300 is not limited to four diodesegments of alternating orientation. In various embodiments, the opticalwaveguide 300 includes many instances of the configuration of the firstdiode segment 341 and the configuration of the second diode segment 342repeated in an alternating manner along the length of the opticalwaveguide 300. In some embodiments, neighboring diode segments (341/342,342/343, 343/344, etc.) of alternate orientation are contiguous witheach other in the lengthwise direction of the optical waveguide 300. Forexample, the second diode segment 342 is contiguous with the first diodesegment 341 in the lengthwise direction of the optical waveguide 300,such that the P-doped region 317 is contiguous with the N-doped region313, and such that the N-doped region 319 is contiguous with the P-dopedregion 315. Also, the third diode segment 343 is contiguous with thesecond diode segment 342 in the lengthwise direction of the opticalwaveguide 300, such that the N-doped region 321 is contiguous with theP-doped region 317, and such that the P-doped region 323 is contiguouswith the N-doped region 319. Also, the fourth diode segment 344 iscontiguous with the third diode segment 343 in the lengthwise directionof the optical waveguide 300, such that the P-doped region 325 iscontiguous with the N-doped region 321, and such that the N-doped region327 is contiguous with the P-doped region 323.

In some embodiments, each of the first electrical conductor 329, thesecond electrical conductor 331, the third electrical conductor 333, thefourth electrical conductor 335, the fifth electrical conductor 337, andthe sixth electrical conductor 339 is formed from material(s) used toform low-resistance electrical contacts in silicon. In some embodiments,each of the first electrical conductor 329, the second electricalconductor 331, the third electrical conductor 333, the fourth electricalconductor 335, the fifth electrical conductor 337, and the sixthelectrical conductor 339 is formed substantially outside of the opticalwaveguide 300. In some embodiments, each of the first electricalconductor 329, the second electrical conductor 331, the third electricalconductor 333, the fourth electrical conductor 335, the fifth electricalconductor 337, and the sixth electrical conductor 339 is formed tosubstantially overlap each of the doped regions to which it iselectrically connected. In some embodiments, the first electricalconductor 329, the third electrical conductor 333, and the fifthelectrical conductor 337 are replaced by a layer of silicide thatextends continuously over the N-doped region 313, the P-doped region317, the N-doped region 321, and the P-doped region 325. Similarly, insome embodiments, the second electrical conductor 331, the fourthelectrical conductor 335, and the sixth electrical conductor 339 arereplaced by a layer of silicide that extends continuously over theP-doped region 315, the N-doped region 319, the P-doped region 323, andthe N-doped region 327.

FIG. 4D shows the top view of the optical waveguide 300 of FIG. 4A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region 103 by the diodes of the first diodesegment 341, the second diode segment 342, the third diode segment 343,and the fourth diode segment 344, in accordance with some embodiments.The first intrinsic electric field E1 in the first diode segment 341pulls the free-carrier electrons (e) out of the core region 103 to theN-doped region 313, and pulls the free-carrier holes (h) out of the coreregion 103 to the P-doped region 315. The second intrinsic electricfield E2 in the second diode segment 342 pulls the free-carrierelectrons (e) out of the core region 103 to the N-doped region 319, andpulls the free-carrier holes (h) out of the core region 103 to theP-doped region 317. The third intrinsic electric field E3 in the thirddiode segment 343 pulls the free-carrier electrons (e) out of the coreregion 103 to the N-doped region 321, and pulls the free-carrier holes(h) out of the core region 103 to the P-doped region 323. The fourthintrinsic electric field E4 in the fourth diode segment 344 pulls thefree-carrier electrons (e) out of the core region 103 to the N-dopedregion 327, and pulls the free-carrier holes (h) out of the core region103 to the P-doped region 325. The first electrical conductor 329 andthe second electrical conductor 331 facilitate completion of anelectrical circuit between the first diode segment 341 and the seconddiode segment 342. The second electrical conductor 333 and the thirdelectrical conductor 335 facilitate completion of an electrical circuitbetween the second diode segment 342 and the third diode segment 343.The fifth electrical conductor 337 and the sixth electrical conductor339 facilitate completion of an electrical circuit between the thirddiode segment 343 and the fourth diode segment 344.

The intrinsic electric fields E1-E4 across the optical waveguide 300sweep out free-carriers that are generated within the core region 103 byTPA. By removing these free-carriers from the core region 103, thefree-carrier concentration in the core region 103 stays low, whichminimizes optical losses within the core region 103 due to free-carrierabsorption. The orientations (perpendicular to the lengthwise centerline106 of the optical waveguide 300) of the first, second, third, andfourth diode segments 341, 342, 343, 344, respectively, are alternatedso as to close the electrical current loops created by the free-carriersweep-out from the core region 103. It should be understood that withoutalternating the orientations of neighboring ones of the first, second,third, and fourth diode segments 341, 342, 343, 344, respectively, theelectrical current generated by the sweep-out of TPA-generatedfree-carriers from the core region 103 would create an electrical chargebuild-up at the sides of the optical waveguide 300 that would counteractthe built-in voltages of the first, second, third, and fourth diodesegments 341, 342, 343, 344, respectively, and correspondinglyshutdown/prevent free-carrier sweep-out from the core region 103.Therefore, by alternating the orientations of the first, second, third,and fourth diode segments 341, 342, 343, 344, respectively, along thelength of the optical waveguide 300, the electrical current generated byfree-carrier sweep-out in a given one of the diode segments 341, 342,343, 344 is balanced by the electrical current generated in neighboringdiode segments.

For example, in the example of FIG. 4D, the electrical current generatedby free-carrier sweep-out in the first diode segment 341 is balanced bythe electrical current generated by free-carrier sweep-out in the seconddiode segment 342. The first electrical conductor 329 and the secondelectrical conductor 331 facilitate balancing of electrical currentsbetween the first diode segment 341 and the second diode segment 342.Also, the electrical current generated by free-carrier sweep-out in thesecond diode segment 342 is balanced by the electrical current generatedby free-carrier sweep-out in the first diode segment 341 and the thirddiode segment 343. The third electrical conductor 333 and the fourthelectrical conductor 335 facilitate balancing of electrical currentsbetween the second diode segment 342 and the third diode segment 343.Also, the electrical current generated by free-carrier sweep-out in thethird diode segment 343 is balanced by the electrical current generatedby free-carrier sweep-out in the second diode segment 342 and the fourthdiode segment 344. The fifth electrical conductor 337 and the sixthelectrical conductor 339 facilitate balancing of electrical currentsbetween the third diode segment 343 and the fourth diode segment 344.Also, the electrical current generated by free-carrier sweep-out in thefourth diode segment 344 is balanced by the electrical current generatedby free-carrier sweep-out in the third diode segment 343.

The alternating orientations of the first, second, third, and fourthdiode segments 341, 342, 343, 344, respectively, along the length of theoptical waveguide 300 avoids the need for having additional electricalinterconnection structures around the optical waveguide 300. In theoptical waveguide 300, the electrical field used to sweep outfree-carriers from the core region 103 is the intrinsic (built-in)electrical field of the PN diode junctions within each of the first,second, third, and fourth diode segments 341, 342, 343, 344,respectively. In some embodiments, because the electrical currentgenerated by TPA within the core region 103 results in a voltage dropacross the optical waveguide 300, which would tend to counter thefree-carrier sweep-out effect, the respective lengths of the diodesegments 341, 342, 343, 344, etc. along the optical waveguide 300 aremade smaller to enhance the electrical current balancing betweenneighboring ones of the diode segments 341, 342, 343, 344, etc. havingopposite orientations across the optical waveguide 300. Also, in someembodiments, some of the different diode segments 341, 342, 343, 344,etc. along the optical waveguide 300 have different lengths, as measuredparallel to the lengthwise centerline 106 of the optical waveguide 300.In some embodiments, the different lengths of the different diodesegments 341, 342, 343, 344, etc. along the optical waveguide 300 aredefined to compensate for an electrical current density imbalancebetween the different diode segments 341, 342, 343, 344, etc.

In some embodiments, optical decay along the optical waveguide 300 willaffect the TPA electrical current generation and create an electricalcurrent imbalance which will result in a small voltage drop across theoptical waveguide 300 between the first cladding region 102 and thesecond cladding region 104. In some embodiments, the lengths of thedifferent diode segments 341, 342, 343, 344, etc. along the opticalwaveguide 300 are defined to compensate for the electrical currentdensity differences (imbalances) along the optical waveguide 300 causedby the optical decay effect on TPA electrical current generation.Therefore, in some embodiments, the lengths of the different diodesegments 341, 342, 343, 344, etc. along the optical waveguide 300 aredefined to improve electrical current balance along the length of theoptical waveguide 300, which provides for reduction in voltage build-upbetween the first cladding region 102 and the second cladding region 104along the length of the optical waveguide 300.

It should be understood that, in some embodiments, the optical waveguide300 provides a silicon optical waveguide structure having reducedTPA-driven optical power loss at high optical power. As described withregard to FIGS. 4A-4D, in some embodiments, the optical waveguide 300 isa rib-shaped optical waveguide structure that is doped on each side tocreate multiple diode structures of alternating orientation along thelength of the optical waveguide 300. Also, it should be understood that,in some embodiments, the optical waveguide 300 is constructed withminimal to no additional electrical interconnection structures near oron the optical waveguide 300, which is beneficial at least because suchadditional electrical interconnection structures could potentiallyoptically interfere with light traveling through the optical waveguide300. In particular, in some embodiments, the optical waveguide 300 doesnot require routing of metal traces over the core region 103 in order toshort the diode terminals of the diode segments 341, 342, 343, 344, etc.along the length of the optical waveguide 300. In some embodiments, eachof the diode segments 341, 342, 343, 344, etc. of the optical waveguide300 is not connected to any electrical circuit external to the opticalwaveguide 300.

FIG. 5A shows a top view of an optical waveguide 500, in accordance withsome embodiments. FIG. 5B shows a vertical cross-section view throughthe optical waveguide 500, referenced as View A-A in FIG. 5A, inaccordance with some embodiments. FIG. 5C shows a vertical cross-sectionview through the optical waveguide 500, referenced as View B-B in FIG.5A, in accordance with some embodiments. FIG. 5D shows a verticalcross-section view through the optical waveguide 500, referenced as ViewC-C in FIG. 5A, in accordance with some embodiments. FIG. 5E shows avertical cross-section view through the optical waveguide 500,referenced as View D-D in FIG. 5A, in accordance with some embodiments.FIG. 5F shows a vertical cross-section view through the opticalwaveguide 500, referenced as View E-E in FIG. 5A, in accordance withsome embodiments.

The optical waveguide 500 is a modification of the optical waveguide 100of FIGS. 1A-1B. The optical waveguide 500 includes the core region 103,the first cladding region 102, and the second cladding region 104 asdescribed with regard to FIGS. 1A-1B. The first cladding region 102 isformed along a first side of the core region 103. The second claddingregion 104 is formed along a second side of the core region 103. Theoptical waveguide 500 includes a diode segment 517 that includes aportion of the core region 103, a portion of the first cladding region102, and a portion of the second cladding region 104. It should beunderstood that for ease of description FIG. 5A depicts a portion of theoptical waveguide 500. In some embodiments, multiple instances of thediode segment 517 are formed along the length of the optical waveguide500.

The optical waveguide 500 includes an N-doped region 501, a P-dopedregion 507, and an intrinsic region 502 located between the N-dopedregion 501 and the P-doped region 507. The N-doped region 501 includes afirst lengthwise section formed 501A within the first cladding region102, a second lengthwise section 501B formed within the second claddingregion 104, and a crosswise section 501C formed to extend between thefirst lengthwise section 501A and the second lengthwise section 501B ofthe N-doped region 501. The P-doped region 507 includes a firstlengthwise section 507A formed within the second cladding region 104, asecond lengthwise section 507B formed within the first cladding region102, and a crosswise section 507C formed to extend between the firstlengthwise section 507A and the second lengthwise section 507B of theP-doped region 507. A first electrical conductor 503 is disposed toelectrically connect the first lengthwise section 501A of the N-dopedregion 501 and the second lengthwise section 507B of the P-doped region507 at a location above the first cladding region 102. A secondelectrical conductor 509 is disposed to electrically connect the firstlengthwise section 507A of the P-doped region 507 and the secondlengthwise section 501B of the N-doped region 501 at a location abovethe second cladding region 104. The first lengthwise section 501A of theN-doped region 501, the first lengthwise section 507A of the P-dopedregion 507, and the intrinsic region 502 collectively form a PIN diodeacross the optical waveguide 500.

The first electrical conductor 503 and the second electrical conductor509 collectively close an electrical circuit between the N-doped region501 and the P-doped region 507. In some embodiments, the firstelectrical conductor 503 is formed as a region of silicide, and thesecond electrical conductor 509 is formed as another region of silicide.In some embodiments, the first electrical conductor 503 is formed as anelectrically conductive structure disposed on an outer portion of thefirst cladding region 102, and the second electrical conductor 509 isformed as an electrically conductive structure disposed on an outerportion of the second cladding region 104. The diode segment 517 isconfigured to form a diode across the optical waveguide 500 such that anintrinsic electric field E extends across the diode segment 517 from theN-doped region 501 to the P-doped region 507 in a direction 551substantially perpendicular to the lengthwise centerline 106 of theoptical waveguide 500. The built-in voltage of the diode segment 517provided by the N-doped region 501 and the P-doped region 507establishes the intrinsic electric field E across the diode segment 517,and particularly across the core region 103 within the diode segment517. In some embodiments, the intrinsic region 502 includes an entiretyof the core region 103 within the diode segment 517, a portion of thefirst cladding region 102 within the diode segment 517, and a portion ofthe second cladding region 104 within the diode segment 517. It shouldbe understood that the core region 103 is present in the intrinsicregion 502 where the intrinsic electric field E is high. The width ofthe intrinsic region 502 is created wide enough so as to avoid overlapof the N-doped region 501 and the P-doped region 507 within the opticalwaveguide 500.

FIG. 5G shows the top view of the optical waveguide 500 of FIG. 5A withdepiction of how free-carriers (electrons (e) and holes (h)) arepulled/swept out of the core region 103 by the diode segment 517, inaccordance with some embodiments. The intrinsic electric field E in thediode segment 517 pulls the free-carrier electrons (e) out of the coreregion 103 to the N-doped region 501, and pulls the free-carrier holes(h) out of the core region 103 to the P-doped region 507. The intrinsicelectric field E across the optical waveguide 500 sweeps outfree-carriers that are generated within the core region 103 by TPA. Byremoving these free-carriers from the core region 103, the free-carrierconcentration in the core region 103 stays low, which minimizes opticallosses within the core region 103 due to free-carrier absorption. Thefirst electrical conductor 503 and the second electrical conductor 509facilitate completion of an electrical current loop within the diodesegment 517, so that the electrical current generated by the sweep-outof TPA-generated free-carriers from the core region 103 does not createan electrical charge build-up at the sides of the optical waveguide 500that would counteract the built-in voltage of the diode segment 517, andcorrespondingly shutdown/prevent free-carrier sweep-out from the coreregion 103.

Also, it should be understood that the electrical current loop withinthe diode segment 517 is closed using the crosswise section 501C of theN-doped region 501 and the crosswise section 507C of the P-doped region507. In some embodiments, each of the crosswise section 501C and thecrosswise section 507C is formed as a thin-doped region conductivechannel that crosses the core region 103 of the optical waveguide 500.In some embodiments, such as shown in FIGS. 5A-5G, the crosswise section501C and the crosswise section 507C are placed on opposite sides of thediode segment 517. In various embodiments, as an alternative to havingthe crosswise sections 501C and 507C, one or more thin doped regionconductive channel(s) like the crosswise sections 501, 507C can beplaced at different positions along the waveguide structure 500, wherethe thin doped region conductive channel(s) is/are P-doped or N-doped.In some embodiments, as an alternative to having both the crosswisesection 501C and the crosswise section 507C, a thin doped regionconductive channel is positioned on one side of the diode segment 517.In some embodiments, as an alternative to having the crosswise sections501C and 507C, a thin doped region conductive channel is positionedsubstantially in the center of the diode segment 517. Also, in someembodiments, thin doped region conductive channels are periodicallypositioned along the diode segment 517.

It should be understood that, in some embodiments, the optical waveguide500 provides a silicon optical waveguide structure having reducedTPA-driven optical power loss at high optical power. It should beunderstood that, in some embodiments, the optical waveguide 500 isconstructed with minimal to no additional electrical interconnectionstructures near or on the optical waveguide 500, which is beneficial atleast because such additional electrical interconnection structurescould potentially optically interfere with light traveling through theoptical waveguide 500. In particular, in some embodiments, the opticalwaveguide 500 does not require routing of metal traces over the coreregion 103 in order to short the diode terminals of the diode segment517. In some embodiments, the diode segment 517 of the optical waveguide500 is not connected to any electrical circuit external to the opticalwaveguide 500.

FIG. 6 shows a flowchart of a method for reducing optical loss within anoptical waveguide (200, 300), in accordance with some embodiments. Themethod includes an operation 601 for having an optical waveguide (200,300) that includes a core region (103), a first cladding region (102),and a second cladding region (104). The core region 103 extendssubstantially along a lengthwise centerline (106) of the opticalwaveguide (200, 300) that corresponds to a light propagation direction(149) through the optical waveguide (200, 300). The first claddingregion (102) is formed along a first side of the core region (103). Thesecond cladding region (104) is formed along a second side of the coreregion (103). The optical waveguide (200, 300) includes a first diodesegment (241, 341) and a second diode segment (242, 342) that eachincludes respective portions of the core region (103), the firstcladding region (102), and the second cladding region (104). The seconddiode segment (242, 342) is contiguous with the first diode segment(241, 341). The first diode segment (241, 341) is configured to form afirst diode across the optical waveguide (200, 300), such that a firstintrinsic electric field (E1) extends across the first diode segment(241, 341) in a first direction substantially perpendicular to thelengthwise centerline (106) of the optical waveguide (200, 300). Thesecond diode segment (242, 342) is configured to form a second diodeacross the optical waveguide (200, 300), such that a second intrinsicelectric field (E2) extends across the second diode segment (242, 342)in a second direction opposite the first direction. The opticalwaveguide (200, 300) includes a first electrical conductor (229, 329)disposed to electrically connect the first diode segment (241, 341) andthe second diode segment (242, 342) at a location on the first side ofthe core region (103). The optical waveguide (200, 300) includes asecond electrical conductor (231, 331) disposed to electrically connectthe first diode segment (241, 341) and the second diode segment (242,342) at a location on the second side of the core region (103). Themethod also includes an operation 603 for transmitting light through thecore region (103) of the optical waveguide (200, 300), such that some ofthe light generates free-carriers (electrons and holes) within the coreregion (103), where the generated free-carriers are swept out of thecore region (103) within the first diode segment (241, 341) of theoptical waveguide (200, 300) by the first intrinsic electric field (E1),and where the generated free-carriers are swept out of the core region(103) within the second diode segment (242, 342) of the opticalwaveguide (200, 300) by the second intrinsic electric field (E2). Itshould be understood that the method of FIG. 6 further includes anyadditional operations corresponding to operation and use of the opticalwaveguides 200 and 300 described herein.

FIG. 7 shows a flowchart of a method for manufacturing an opticalconveyance device, in accordance with some embodiments. The methodincludes an operation 701 for forming an optical waveguide (200, 300)that includes a core region (103), a first cladding region (102), and asecond cladding region (104). The core region (103) extendssubstantially along a lengthwise centerline (106) of the opticalwaveguide (200, 300) that corresponds to a light propagation direction(149) through the optical waveguide (200, 300). The first claddingregion (102) is formed along a first side of the core region (103). Thesecond cladding region (104) is formed along a second side of the coreregion (103). The method also includes an operation 703 for forming afirst diode within a first diode segment (241, 341) of the opticalwaveguide (200, 300). The first diode segment (241, 341) includes afirst portion of the core region (103), a first portion of the firstcladding region (102), and a first portion of the second cladding region(104). The first diode includes an N-doped region (213, 313) formedwithin the first portion of the first cladding region (102) and aP-doped region (215, 315) formed within the first portion of the secondcladding region (104), such that a first intrinsic electric field (E1)extends through the first portion of the core region (103) in a firstdirection substantially perpendicular to the lengthwise centerline (106)of the optical waveguide (200, 300). The method also includes anoperation 705 for forming a second diode within a second diode segment(242, 342) of the optical waveguide (200, 300). The second diode segment(242, 342) includes a second portion of the core region (103), a secondportion of the first cladding region (102), and a second portion of thesecond cladding region (104). The second diode includes a P-doped region(217, 317) formed within the second portion of the first cladding region(102) and an N-doped region (219, 319) formed within the second portionof the second cladding region (104), such that a second intrinsicelectric field (E2) extends through the second portion of the coreregion (103) in a second direction opposite of the first direction. Themethod also includes an operation 707 for electrically connecting theN-doped region (213, 313) of the first diode to the P-doped region (217,317) of the second diode. The method also includes an operation 709 forelectrically connecting the P-doped region (215, 315) of the first diodeto the N-doped region (219, 319) of the second diode. It should beunderstood that the method of FIG. 7 further includes any additionaloperations corresponding to manufacturing of the optical waveguides 200and 300 described herein.

The foregoing description of the embodiments has been provided forpurposes of illustration and description, and is not intended to beexhaustive or limiting. Individual elements or features of a particularembodiment are generally not limited to that particular embodiment, but,where applicable, are interchangeable and can be used in a selectedembodiment, even if not specifically shown or described. In this manner,one or more features from one or more embodiments disclosed herein canbe combined with one or more features from one or more other embodimentsdisclosed herein to form another embodiment that is not explicitlydisclosed herein, but rather that is implicitly disclosed herein. Thisother embodiment may also be varied in many ways. Such embodimentvariations are not to be regarded as a departure from the disclosureherein, and all such embodiment variations and modifications areintended to be included within the scope of the disclosure providedherein.

Although some method operations may be described in a specific orderherein, it should be understood that other housekeeping operations maybe performed in between method operations, and/or method operations maybe adjusted so that they occur at slightly different times orsimultaneously or may be distributed in a system which allows theoccurrence of the processing operations at various intervals associatedwith the processing, as long as the processing of the method operationsare performed in a manner that provides for successful implementation ofthe method.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofthe appended claims. Accordingly, the embodiments disclosed herein areto be considered as illustrative and not restrictive, and are thereforenot to be limited to just the details given herein, but may be modifiedwithin the scope and equivalents of the appended claims.

1. An optical conveyance device, comprising: an optical waveguide; afirst diode formed across the optical waveguide, the first diodeestablishing a first intrinsic electric field across the opticalwaveguide in a first direction; a second diode formed across the opticalwaveguide, the second diode establishing a second intrinsic electricfield across the optical waveguide in a second direction that isopposite the first direction; and an electrical current loop formedacross the optical waveguide through both the first diode and the seconddiode.
 2. The optical conveyance device as recited in claim 1, furthercomprising: a first electrical conductor disposed to connect the firstdiode to the second diode at a first side of the optical waveguide; anda second electrical conductor disposed to connect the first diode to thesecond diode at a second side of the optical waveguide.
 3. The opticalconveyance device as recited in claim 2, wherein the first electricalconductor is connected to both a first doped region of the first diodeand to a first doped region of the second diode, and wherein the secondelectrical conductor is connected to both a second doped region of thefirst diode and to a second doped region of the second diode.
 4. Theoptical conveyance device as recited in claim 3, wherein the first dopedregion of the first diode is N-doped, and the first doped region of thesecond diode is P-doped, and wherein the second doped region of thefirst diode is P-doped, and the second doped region of the second diodeis N-doped.
 5. The optical conveyance device as recited in claim 4,wherein the first doped region of the first diode and the second dopedregion of the first diode are collectively configured to form the firstintrinsic electric field across the optical waveguide in the firstdirection, and wherein the first doped region of the second diode andthe second doped region of the second diode are collectively configuredto form the second intrinsic electric field across the optical waveguidein the second direction.
 6. The optical conveyance device as recited inclaim 4, wherein the first doped region of the first diode and the firstdoped region of the second diode share a first common boundary, andwherein the second doped region of the first diode and the second dopedregion of the second diode share a second common boundary.
 7. Theoptical conveyance device as recited in claim 4, wherein each of thefirst electrical conductor and the second electrical conductor extendscontinuously along an entire length of both the first diode and thesecond diode as measured in a light propagation direction through theoptical waveguide.
 8. The optical conveyance device as recited in claim4, wherein both the first doped region of the first diode and the firstdoped region of the second diode are formed within a first claddingregion of the optical waveguide, and wherein both the second dopedregion of the first diode and the second doped region of the seconddiode are formed within a second cladding region of the opticalwaveguide.
 9. The optical conveyance device as recited in claim 8,wherein the first cladding region includes a first inner cladding regionhaving a first vertical thickness and a first outer cladding regionhaving a second vertical thickness greater than the first verticalthickness, and wherein the second cladding region includes a secondinner cladding region having the first vertical thickness and a secondouter cladding region having the second vertical thickness.
 10. Theoptical conveyance device as recited in claim 9, wherein the firstelectrical conductor is disposed on the first outer cladding region, andwherein the second electrical conductor is disposed on the second outercladding region.
 11. The optical conveyance device as recited in claim10, wherein each of the first doped region of the first diode and thefirst doped region of the second diode is formed within the first outercladding region, and wherein each of the second doped region of thefirst diode and the second doped region of the second diode is formedwithin the second outer cladding region.
 12. The optical conveyancedevice as recited in claim 11, wherein each of the first doped region ofthe first diode and the first doped region of the second diode ispartially formed within a portion of the first inner cladding region,and wherein each of the second doped region of the first diode and thesecond doped region of the second diode is partially formed within thesecond inner cladding region.
 13. The optical conveyance device asrecited in claim 11, wherein the optical waveguide includes a coreregion located between the first inner cladding region of the opticalwaveguide and the second inner cladding region of the optical waveguide.14. The optical conveyance device as recited in claim 13, wherein thecore region of the optical waveguide has a third vertical thicknessgreater than the first vertical thickness.
 15. The optical conveyancedevice as recited in claim 14, wherein the third vertical thickness issubstantially equal to the second vertical thickness.
 16. The opticalconveyance device as recited in claim 1, wherein the first diode and thesecond diode are formed adjacent to each other along a length of theoptical waveguide as measured in a light propagation direction throughthe optical waveguide.
 17. The optical conveyance device as recited inclaim 16, wherein the first diode is one of a plurality of instances ofthe first diode formed along the length of the optical waveguide, andwherein the second diode is one of a plurality of instances of thesecond diode formed along the length of the optical waveguide, andwherein plurality of instances of the first diode and the plurality ofinstances of the second diode are formed in an alternating manner alongthe length of the optical waveguide.
 18. The optical conveyance deviceas recited in claim 17, wherein a length of each of the plurality ofinstances of the first diode as measured in the light propagationdirection along the optical waveguide is substantially equal to a lengthof each of the plurality of instances of the second diode as measured inthe light propagation direction along the optical waveguide.
 19. Theoptical conveyance device as recited in claim 17, wherein each of theplurality of instances of the first diode has a respective length asmeasured in the light propagation direction along the optical waveguide,and wherein each of the plurality of instances of the second diode has arespective length as measured in the light propagation direction alongthe optical waveguide, and wherein the respective lengths of theplurality of instances of the first diode and the respective lengths ofthe plurality of instances of the second diode are configured tocompensate for two-photon-absorption-induced electrical current densitydifferences along the optical waveguide.
 20. The optical conveyancedevice as recited in claim 1, wherein the optical waveguide includes acurved portion, and wherein the first diode and the second diode areformed within the curved portion of the optical waveguide.